This is a general overview of fitting a Quaife differential to an ATV code gearbox that is the standard G40 gearbox. This is more of a follow on guide to the one Paul Hayes produced on fitting the “Gripper” LSD into his ATV gearbox previously equipped “Gemini” LSD Gearbox. The reason I produced this guide is there are few slight differences that may be encountered when fitting a Quaife differential to a standard ATV gearbox.

Before reading on, I would like to point out that I can’t be held responsible for anyone who follows any of the advice or instructions within this guide. These views and instruction are totally my own views and anyone using this guide takes responsibility for their own actions.

Time required.

This is not a quick job and I’m sure if you have already read Paul’s guide, you will understand this. Plan to have the gearbox stripped down for two to three days depending on how quick you work and how quickly you can get the new differential fitted washer you will order later.

This assumes that the gearbox is removed from the car and all of the gear oil is drained out. If the gear oil isn’t drained out or you think there may be some left in there, get it mounted on a bench so a container can under the drain plug, then drain it out. Sit the gearbox on your workbench.

Loosen the driveshaft flange cup bolts with the correct hex socket which are mounted in the centre of the driveshaft flange cups. If you can’t see them, it’s because theres too much CV grease in there, so get it wiped out !

Once the bolts are withdrawn, the driveshaft flange cups will simply draw out. Watch out for any gear oil that may emerge. Put these to one side, preferably in your de-greasing tank ready to be cleaned at a later stage. Sit the gearbox clutch housing side up.

Undo the gearbox casing screws that hold the two halves together, I work around by loosening them progressively and then withdraw them. Put them to one side for later. Now the casing should separate with a bit of persuasion. Lift the clutch housing side off and put it to one side. You will now be looking inside your gearbox, more importantly, your diff assembly. The diff assembly will lift out, do this and take it to where you are working.

You will need a number of parts from the diff assembly, mainly including the crown wheel, press fit bolts, nuts, packing plates and speedo drive gear. Unlike the guide to fitting the “Gripper” diff, you will need to keep the press fit bolts, nuts and packing plates. You may prefer to replace the press fit bolts and nuts, but they are expensive. The press fit bolts are currently £2.59 each and the nuts are currently £4.17 each (bear in mind there are six off, of each) plus VAT from VW. The reason for the high price is the unusual thread diameter and pitch.

Sit your diff assembly in a vice with soft jaws and start by removing the bearing from the end with the plastic speedo drive ring (as you need to keep this). You can buy a new speedo drive ring from VAG quite easily, if you are doing this move on to removing the crown wheel. Get your bearing sperator on, split the bearing away from the diff then use the puller on it. Now you can withdraw the speedo drive ring, keep it to one side.

Turn the diff around and put it in the vice with the crown wheel nuts facing up, use soft jaws to avoid damaging the diff. I found that a ½” socket fitted the nuts better than a 13mm socket (as most folk might only have metric). Go around the six nuts and progressively undo them, and withdraw them once loose. Remove the three packing plates and keep them to one side with the nuts.

Now the crown wheel can be removed from the differential. This may seem really straightforward as you try and pull it off the diff. But you will find it’s fairly tight on the diff. Don’t be tempted to heat the crown wheel up to expand it so it comes off more easily as this may affect any heat treatment and/or change the surface properties that it had when it was made.

With diff in the vice, the crown wheel needs tapping upwards to get it off. I used a solid bar of aluminium, you could use brass if you wan’t (as they are both fairly soft and won’t easily damage the crown wheel). Exercise caution and start tapping the up crown wheel on the outer edge, but don’t go hitting on the teeth of the wheel as you don’t wan’t to chip or damage them. A couple of taps each side and it will start moving up and you will soon have it removed.

Now the press fit bolts need removing from the diff (unless you are buying new ones). Get your selection of parallel punches and hammer at the ready and find one of the punches thats just under the diameter of the bolt. Make sure when you hit the bolts out of the diff that you do it squarely, straight and not on the edges of the bottom of the bolt as you may damage the thread. Again, make sure the diff it secure in the vice, preferably with soft jaws. Hit all six press fit bolts out (they take a fair bit of hitting, but will go) and recover them with the lock plates (on two of them). Be careful with the diff now as the pinions could fall out (by removing the lock plates). Knock the two bolts from the lock plates that have them fitted. Put the old diff away now you have removed everything you need from it.

Now get your nice, new, shiny Quaife diff at the ready. I fitted the speedo drive ring and bearings first, but you could fit the crown wheel first, should you wish. Get the two new VAG differential bearings at the ready and a marker pen ready. The taper roller bearings have the main bearing and an outer race. I put a dot on one outer race and bearing (narrow end of cone) so I knew I had the correct corresponding bearing and race. Keep the outer races in the freezer overnight (prior to doing this) and put the kettle on for the bearings, make yourself a brew aswell !

As a side note, I compared the prices of the genuine VAG bearings to aftermarket ones of the same brand from a bearing supplies, and they were more expensive at the bearing supplies ! (plus you have the hassle of finding the correct size and fit there) so it’s a no brainer for me.

Drop the speedo drive ring onto the quaife diff so it sits in the notches. I noticed that it fitted better than onto the standard diff ! Pour your self some boiling water into a suitable receptacle (I used an empty glass jar) and put the bearing into the boiling water for a couple of minutes. I dropped it in with a piece of wire so I could easily retrieve it, then wipe clean the bearing surface of the diff (it may have some grease on it). Whip the bearing out of the water and let water run off, then put the bearing onto the diff ensuring it’s sat square to it. I found they just pushed home by a fair tap the palm of my hand. repeat again for the bearing on the opposite side.

Now the crown wheel bolts can be fitted to the quaife diff. Ensure the crown wheel, press fit bolts, packing plates and nuts are de-greased and are totally clean and dry before doing this. Firstly the press fit bolts have to be put into the quaife diff, so put the diff into a vice with soft jaws or similar (so it won’t get marked) facing so the bolts will go in. Knock them in using a fairly big parallel punch (no bigger than the head diameter) until they are flush with the surface. Repeat until all six are in you are happy they are sitting straight.

Turn the diff up so the crown wheel can be offered on, you may find it is a fairly close fit (not quite a press fit, though) and double check all mating surfaces are totally clean. Tap around the perimeter again, using a soft drift like the aluminium bar, avoiding the teeth and you should start to see it go onto the diff. Keep going until it’s fully there. Now you can put the packing plates on, ready for the nuts. Before putting the nuts on, ensure the diff is well clamped, but not in a way that damages it, and you have your torque wrench to hand.

Put a dab of the loctite 243 thread lock on the threads, enough to fill the nut threads, not so it splurges everywhere ! Wind all the nuts down. Get your torque wrench and set it to 70 Nm or 51.6 Lb/ft with the ½” socket fitted. Progressively tighten them all around until the final torque is achieved. Now the diff is assembled, leave it to one side for now while the thread lock sets.

I would only recommend a medium strength thread lock that is oil tolerant, hence the one I chose. Permanent or strong is overkill in my opinion as the base of the nuts are serrated anyway to stop from turning. It’s only the fact that Quaife specify you should use thread lock, that you do.

The old outer bearing races are still to be removed from the gearbox casings, this in the same way Paul did in his guide. Knock the old diff oil seals out, with a punch or similar, taking care. With the races, I used a parallel punch and made sure it sat in the lip of the bearing outer race (it’s a bit more fiddly, but worth it) so you don’t hit the washer as there is a chance you can chip or gouge it with the punch. You don’t want to damage the fitted washer on the gearbox side as this one is kept and fitted with the new outer race. Keep the fitted washer for the gearbox end to one side and label it. Also keep one of the old outer races as you will see why next. Clean the mating faces of the casings using, cloth, a razor scraper and de-greaser until no gasket sealer, oil or foreign matter is left.

Retrieve the new outer races from your freezer so they will have shrunk well enough to knock them in. Clean both bearing housings and drop the gearbox side fitted washer in place. Identify which race is for which bearing offer, up the new, cleaned races and start to tap them in square with an old race for the gearbox one. For the clutch housing carefully tap in with a 3/8” drive extension or parallel punch (note no fitted washer behind the race).

The diff can be temporarily fitted to the gearbox and the clutch housing case fitted. Put all the screws in, go around and nip them up for now. I found it easier with the clutch housing facing up to set the dial gauge up. Use a piece of steel strip secured somewhere so you can get your dial gauge and stand mounted to measure the free play in the diff. Free play in the diff is measured in the same way as Paul’s guide to fitting the Gripper or standard diff. Sit the dial gauge on top of the diff and zero it, put your fingers under the diff and push up and you will have measured the free play. Make sure the gauge goes back to zero, repeat the check so you know it’s right. The free play in my case was 1.25mm. So you calculate the preload, hence the fitting washer thickness as follows:

Free Play + Pre Load figure = Fitting Washer Thickness

In my case this was:

1.25 + 0.3 = 1.55mm

The washers are available from VAG and cost around 50p plus VAT. There is an exact 1.55mm washer available for mine, which I ordered. Have a look at ETKA or the table in Paul’s guide to doing diff bearings to see which size & part number you require:

I may be worth checking the old washer you took out, incase it is the right size. Otherwise wait until the washer you ordered comes in at your local dealer. When you get the new washer, just check it is the correct thickness to be sure. Use a micrometer or high quality vernier caliper.

Now the casings can be opened up again, ready for the fitted washer. Knock the new diff bearing outer race out from the clutch housing end with a suitable punch, taking care not to chip or damage the race. Drop the new washer in and re-fit the outer race (freeze it again before hand if you wish).

All that is left to do is seal the gearbox up and fit the driveshaft flange cups and seals. Ensure the casing mating surfaces are clean and de-greased ready for the new sealant. Have a read of the manufacturers’ instructions of your gasket sealant. The gasket sealer I used stays liquid in the presence of air, so it won’t set until its trapped between the casings. You only need a small amount with the liquid sealer I used. Make sure its spread around enough to fill the gap when assembled.

Fit the casing screws and tighten to the specified torque which should be in the Haynes manual, let the sealer go off for a while. Now the oil seals can be fitted to the casings by knocking them in flush to the casings with a mallet or something that won’t damage them.

The driveshaft flange cups can be inserted after you have cleaned them up, taking note of which side is which as they are slightly different. I put a tiny bit of the same thread lock I used earlier on the bolts before I fitted them. You will need to lock the driveshaft flange cups from turning when you torque them up. Possibly the easiest way is putting a bar in between two driveshaft screws temporarily fitted to the outer flange. Be careful doing this, the flange to diff bolts are only 25 Nm so not a huge torque to worry about. Torque them both up and then that’s the it !